The dynamic setting and processes of tectonic and magmatic evolution of the oblique collision zone between Indian and Eurasian plates: Exemplified by the tectonic evolution of the Three River region, eastern Tibet
印度-欧亚侧向碰撞带构造-岩浆演化的动力学背景与过程——以藏东三江地区构造演化为例

Through detailed structural analysis of Cenozoic deformation in the oblique collision zone between Indian and Eurasian plates,i.e.in the Three River region in eastern Tibet,three different structural styles are recognized.They are formed at different crustal levels in Cenozoic: 1)thin-skinned thrust faults and nappe structures developed from outcrop to regional scales.They are widely distributed in the Three River region,especially in Lanping-Simao basin;2)regional high-temperature strike-slip ductile shear zones,exemplified by Red River-Ailao Shan,Lancang River and Nujiang River-Gaoligong Shah shear zones,and local brittle strike- slip faults.The latter are common in the Mesozoic and Cenozoic in Lamping-Simao basin.3)Metamorphic core complexes and graben or half-subgraben basins are distributed all around in a fan-shaped area between the Red River-Ailao Shan and Sagaing shear zones. Regional magmatic activities are closely related to tectonic activities both temporally and spatially.Regional progressive shortening and strike-slip faulting occurred in the early stage of the collision process.They may have triggered the high potassium magmatism with subduction-related characteristics.Late stage progressive extension resulted in high-potassium magmatism of intraplate characteristics. A magmatic gap between the two periods of alkaline magmatic activities is in coincidence with the changing in regional tectonic systems and the occurrence of regional extension,which is shown directly by the exhumation of metamorphic core complexes and weak calc- alkaline magmatic activities.In combination with regional paleo-magnetic data,it is shown that the interaction between Indian and Eurasian plates,the rotation of regional plates and crustal blocks,and hence induced tectonic processes may provide constraints on the occurrence of different geological events.It is suggested that the clockwise and anticlockwise rotation of the northerly moving Indian plate gave rise to two stages of rotation of crustal blocks in the Three River region,an early large angle and high speed rotation and a late small angle and slow rotation.Such rotation of crustal blocks are the major cause of the early stage of progressive shortening, strike-slip faulting,and magmatic arc type alkaline magmatic activities,an intermediate stage of exhumation of metamorphic core complexes and calc-alkaline magmatic activities,and a late stage of progressive extension and intraplate alkaline activities.